Field of the Invention
The present invention pertains generally to centrifugal fans/blower wheels of the type used in HVACR (heating/ventilation/air-conditioning/refrigeration) equipment. More specifically, the present invention pertains to forward-curved centrifugal blower wheels having a unique fan blade configuration that provides improved efficiency over prior art blower wheels.
General Background
Centrifugal blower wheels (sometimes called “squirrel cage” blowers or fans) are commonly used in HVACR equipment to generate air flow. Such blower wheels are typically formed of plastic or metal and comprise a plurality of fan blades circumferentially spaced about the axis of fan rotation. In most cases, the opposite ends of the fan blades are attached to each other via a ring, disk, or plate or some other form of divider or end member. Examples of such include the blower wheels disclosed in U.S. Pat. Nos. 8,881,396 and 5,988,979.
Centrifugal blowers operate by drawing air or other gas axially into the blower wheel parallel to the axis of rotation, and expelling such air or gas through the fan blades via the centrifugal force acting on the air or gas between the fan blades. Some blower wheels are open at both axial ends and are configured to draw air or gas into the blower wheel from both of its axial sides. These are referred to herein as dual inlet blower wheels. Other blower wheels are configured to draw air in from just one of their axial sides (referred to herein as single inlet blower wheels). The present invention pertains to both of such types of blower wheels.
A complete blower assembly may comprise a drive motor positioned partially or completely within the blower wheel, or completely external to the blower wheel. Still further, blower wheels may comprise forward-curved, backward-curved, or straight radial fan blades. The mean camber lines of the fan blades of a forward-curved blower wheel curve in the direction of blower wheel rotation as they extend radially outward. In contrast, backward-curved blades curve in the opposite direction as they extend radially outward. Some fan blades vary in thickness as they extend radially outward. Other fan blades (especially those formed of sheet metal) have a uniform thickness from leading to trailing edges. Regardless, the mean camber lines of the fan blades of a blower wheel define whether the blower wheel has forward-curved, backward-curved, or straight radial fan blades. The present invention pertains to all types of blower fans having forward-curved blower wheels.
It was generally known prior to the present invention that reducing the leading edge blade angle of the fan blades of a forward curved blower wheel should be more efficient. However, it was also known prior to the present invention that reducing the leading blade angle of the fan blades required greater cord length blades, and that in order to keep such a blower wheel from buffeting and operating poorly, which blower wheels having low leading edge blade angle fan blades had a strong tendency to do, the inlet ring of the blower housing had to be made smaller. The smaller inlet ring of the blower housings then offset any potential efficiency gain.